This invention relates to an apparatus and method for controlling the operation of an internal combustion engine, and more particularly, it relates to such an engine control apparatus and method in which operational timing such as ignition timing of a plurality of cylinders of the engine can be controlled based on a reference position signal indicative of predetermined crankshaft angles.
In general, in an internal combustion engine having a plurality of cylinders with a crankshaft and a camshaft operatively connected therewith, a signal generator generates a reference position signal in synchronization with the rotation of the engine, based on which signal operational timing of the engine such as ignition timing, fuel injection timing and the like is determined. It is necessary that the reference position signal exactly indicate predetermined reference positions corresponding to predetermined crank angles.
FIG. 4 illustrates in block form the general arrangement of a known engine control apparatus. In this figure, the known engine control apparatus includes a signal generator 1, a sensor means 2 and a control unit 3, as will be described below in detail. The signal generator 1 generates, in synchronization with the rotation of an engine crankshaft, a crank angle signal .theta. comprising a series of successive pulses and indicative of the rotational position of the crankshaft as well as a reference signal T indicative of a reference position corresponding to a predetermined crank angle of each cylinder. The sensor means 2 includes a plurality of sensors such as an intake air sensor for sensing the amount or flow rate of intake air and generating a corresponding output signal representative of the engine load, a rotational speed sensor for sensing the rotational speed or the number of revolutions per minute of the engine, a temperature sensor for sensing the temperature of intake air, pressure sensors each mounted in a corresponding cylinder for sensing the internal pressure therein, and the like. The control unit 3 in the form of a microcomputer is connected to receive the output signals T, .theta. from the signal generator and the output signal D from the sensor means 2 and determines, based these signals, control timing such as ignition timing for each cylinder to thereby calculate a control time Ta corresponding to the thus determined ignition timing for each cylinder.
Specifically, the control unit 3 includes a reference position setting means 31 for generating a reference position signal T.theta. based on the reference signal T and the crank angle signal .theta., and an ignition timing setting means 32 for determining a control time Ta for each cylinder based on the crank angle signal .theta., the reference position signal T.theta., and the engine operating condition signal D.
The ignition timing setting means 32 includes a position counter for counting the number of pulses in the crank angle signal .theta. until it is reset in response to an occurrence of a reference position of each cylinder for setting a control time Ta from a predetermined reference position to an ignition timing.
FIG. 5 is a perspective view of the signal generator 1. The illustrated signal generator 1 includes a rotating disk 10 which is mounted on a camshaft 9 operatively connected with an unillustrated engine crankshaft for synchronized rotation therewith. The rotating disk 10 has a plurality of circumferentially extending slits 12 disposed at a predetermined pitch, as well as four radial slits disposed apart from each other at equal circumferential intervals. A first pair of light emitter 15 and light receiver 16 are disposed on the opposite sides of the rotating disk 10 in axially aligned relation with each other on a circle on which the circumferential slits 11 lie, in such a manner that during rotation of the disk 10, the circumferential slits 11 pass between the opposed first light emitter 15 and light receiver 16. Similarly, a second pair of light emitter 17 and light receiver 18 are disposed on the opposite sides of the rotating disk 10 in axial alignment with each other in a manner such that during rotation of the disk 10, the radial slits 12 pass between the opposed second light emitter 17 and the second light receiver 18. In the illustrated example, the number of radial slits 12 is four, which corresponds to a four-cylinder engine. When one of the slits 11 becomes aligned with the first light emitter 15 and the first light receiver 16 during rotation of the disk 10, light emitted from the first light emitter 15 passes through the now aligned slit 11 to reach the opposed second light receiver 16 which thereby generates an electric output signal in the form of a crank angle signal .theta.. Similarly, when one of the slits 12 becomes aligned with the second light emitter 17 and the second light receiver 18 during rotation of the disk 10, light emitted from the second light emitter 17 passes through the now aligned slit 12 to reach the opposed second light receiver 18 which thereby generates an electric output signal in the form of a reference signal T.
FIG. 6 illustrates waveforms of the crank angle signal .theta. and the reference signal T generated by the signal generator 1. The pitch or interval between adjacent pulses in the crank angle signal .theta. is set, for example, to about 0.5 degrees, whereas pulses in the reference signal T are sequentially generated at reference positions of cylinders #1, #3, #4 and #2. Accordingly, the rotating disk 10 must be mounted on the camshaft 9 in a precise manner so that each of the slits 12 exactly corresponds to the reference position of a corresponding cylinder, as shown in FIG. 5.
The operation of the known engine control apparatus as described and illustrated in FIG. 4 will now be described in detail with particular reference to FIGS. 5 and 6. As shown in FIG. 6, the signal generator 1 generates, in synchronization with the rotation of the unillustrated crankshaft, a reference signal T and a crank angle signal .theta. which are input to the control unit 3, whereupon the reference position setting means 31 in the control unit 3 generates a reference position signal T.theta. with a crank angle signal .theta., at which the reference signal T rises, being made as a reference position.
The position counter in the ignition timing setting means 32 counts the number of pulses in the crank angle signal .theta. until it is reset when the reference position indicated by the reference position signal T.theta. occurs. The ignition timing setting means 32 determines an optimal ignition timing (i.e., a corresponding crank angle) for each cylinder based on the counted value of the position counter and the engine operating conditions D, and then calculates a control time Ta from the reference position to the thus determined ignition timing. Although at this time, the ignition timing setting means 32 normally calculates the optimal ignition timing based on a preset map which is predetermined in accordance with the engine operating conditions D, a peak position of a cylinder pressure signal contained in the engine operating condition signal D is fed back to the ignition timing setting means 32 so that it is determined, based the cylinder pressure signal, whether ignition has actually taken place at an optimal instant.
With the known engine control apparatus as described above in which the reference position signal T.theta. is determined on the basis of the two different kinds of pulse signals T, .theta. generated by the signal generator 1, two separate sensing systems corresponding, respectively, to the first and second slits 11, 12 are required, thus adding to the cost of manufacture. Moreover, in cases where the rotating disk 10 has to be mounted on the engine crankshaft, it becomes difficult to properly dispose the photocouplers 15 through 18 since a very limited space is usually available around the crankshaft in an engine room of a vehicle. Moreover, in order for the signal generator to generate the reference signal T with a high degree of preciseness, highly precise mounting of the rotating disk 10 with respect to a rotating shaft such as a camshaft, an engine crankshaft and the like is also required.